Radio frequency (RF) power amplifier solutions for cellular base station applications are moving away from single-band single-mode platforms towards multi-band multi-mode platforms in which one power amplifier will be able to cover multiple adjacent frequency bands. In such a platform, the RF power amplifier should be capable of operating over operating frequencies spanning the multiple bands with reasonable performance.
Doherty amplifiers are commonly used for cellular base station applications. However, conventional broadband amplifier designs tend to be limited by impedance dispersion over the covered frequency range. Such high levels of impedance dispersion make such power amplifiers undesirable for broadband Doherty operation. In addition, conventional approaches result in quality factor limitations at the lower end of the band, and relatively large phase linearity variation across the band, both of which may limit Doherty amplifier performance.